1. Field of the Invention
This invention relates to a process for producing alcohol by saccharification and fermentation of a starchy material without cooking.
2. Description of the Prior Art
It is the conventional practice to cook a mash consisting of a slurry of a ground starchy material at high temperatures such as 150.degree. C. [Industrial Fermentation Vol.1, ed by L. A. Underkofler and R. J. Hickey, Chemical Publishing Co., Inc., 1954. p.17., Trans Am. Inst. Chem. Eng., 40, 421 (1944), Food Can., 29, 23 (1969)] The purpose of cooking is to rupture the structure of the raw material grits thereby eluting starch from the grits to avoid a viscosity increase owing to gelatinization after eluting, aid in the actions of liquefying and saccharifying enzymes, and further to kill microorganisms harmful to saccharification and fermentation. After cooking, however, the mash must be cooled to about 25.degree. to 35.degree. C. which is the fermenting temperature, and the energy required for cooling is great. Hence, the total energy consumption including the energy spent for cooking is enormous in the conventional high temperature cooking process.
In recent years, the aggravated supply of energy caused by the increased price of petroleum has prompted much research work for development of new energy sources. In particular, much interest has been aroused in ethanol which can be renewably produced from biomass resources grown under the action of solar energy because it is expected to be a petroleum fuel substitute.
Some of the present inventors previously developed an energy-saving process for producing alcohol which involves cooking at a temperature of 75.degree. to 85.degree. C. (U.S. Pat. No. 4,092,434 issued May 30, 1978, G.B. Pat. No. 1,503,760 issued Mar. 15, 1978).
It is known on the other hand the processes for Japanese sake brewing and alcoholic production without cooking. [1. J. Ferm. Ass. Japan 10 319 (1952), 2. J. Ferm. Ass. Japan 21 83 (1963), 3. J. Ferment. Technol. 58 237 (1980), 4. J. Brew. Soc. Japan 75 858 (1980), 5. Abstract of Papers, Annual Meeting of the Society of Fermentation Technology of Japan, Osaka, November 1980 P4]. However, these techniques require some special operations such as acidification of mash (pH 3.5), which prevents contamination of harmful microorganisms (above-cited 1, 2, 3, 4). And the prior techniques require a longer period of the time for the saccharification and fermentation (above-cited 1, 2, 4, 5) or such prior techniques require complex process steps such as dialysis of a fermented broth (above-cited 3, 4) and are difficult to be accepted industrially.